class person:
    def eat (self):
        print("人吃饭")

class cat :
    def eat (self):
        print("猫吃鱼")

class dog :
    def eat (self):
        print("狗啃骨头")

per=person()
cat1=cat()
dog1=dog()

def eat (obj):
    obj.eat()

eat(per)
eat(cat1)
eat(dog1)